A Methodist from age ten, and later a fundamentalist Baptist, Gish believed that the Biblical creation story was historical fact.[7] After reading the booklet Evolution, "Science Falsely So-called" in the late 1950s, Gish became persuaded that science had produced falsifying evidence against biological evolutionary theory and that various fields of science offered corroborating evidence in support of the Biblical creation story.[8] He joined the American Scientific Affiliation (ASA), an association of Christian scientists, mistakenly assuming the group supported creationism. Through his affiliation at the ASA, Gish met geneticist and creationist, William J. Tinkle, who in 1961 invited Gish to join a newly formed anti-evolution caucus within the ASA.[7]

Debating opponents said that Gish used a rapid-fire approach during a debate, presenting arguments and changing topics quickly. Eugenie Scott, executive director of the National Center for Science Education, dubbed this approach the "Gish Gallop," describing it as "where the creationist is allowed to run on for 45 minutes or an hour, spewing forth torrents of error that the evolutionist hasn't a prayer of refuting in the format of a debate."[11] She also criticized Gish for failing to answer objections raised by his opponents.[12] The phrase has also come to be used as a pejorative to describe similar debate styles employed by proponents of other, usually fringe beliefs, such as homeopathy or the moon landing hoax.[13][14]

Gish was also criticised for using a standardized presentation during debates. While undertaking research for a debate with Gish, Michael Shermer noted that Gish used similar openings, assumptions about his opponent, slides, and even jokes. Although Shermer said that while he stated he was not an atheist and was willing to accept the existence of a divine creator, Gish attempted to prove that Shermer was indeed an atheist and therefore immoral.[15]Massimo Pigliucci, who debated Gish five times, said that he ignored evidence contrary to his religious beliefs.[16] One opponent accused Gish of stonewalling arguments with fabricated data.[17]

Some creationists view Gish's performances differently. In the early days of his debates, one creationist wrote, "evolutionists were caught somewhat by surprise when a qualified speaker—complete with a working knowledge of the relevant literature and research—challenged their worldview.... Soon spokespersons for evolution publicly recommended that evolutionists not debate Duane Gish because they would surely lose."[4]